A power switch-mode power converter (also referred to as a “power converter” or “regulator”) is a power supply or power processing circuit that converts an input voltage waveform into a specified output voltage waveform. DC-DC power converters convert a dc input voltage into a dc output voltage. Controllers associated with the power converters manage an operation thereof by controlling the conduction periods of power switches employed therein. Generally, the controllers are coupled between an input and output of the power converter in a feedback loop configuration (also referred to as a “control loop” or “closed control loop”).
Typically, the controller measures an output characteristic (e.g., an output voltage, an output current, or a combination of an output voltage and an output current) of the power converter, and based thereon modifies a duty cycle of the power switches of the power converter. The duty cycle is a ratio represented by a conduction period of a power switch to a power switching period thereof. Thus, if a power switch conducts for half of the power switching period, the duty cycle for the power switch would be 0.5 (or 50%). Additionally, as voltage or current for systems, such as a microprocessor powered by the power converter, dynamically change (e.g., as a computational load on the microprocessor changes), the controller should be configured to dynamically increase or decrease the duty cycle of the power switches therein to maintain an output characteristic such as an output voltage at a desired value.
In an exemplary application, the power converters have the capability to convert an unregulated input voltage supplied by an input voltage source, such as a battery, to a higher or lower, regulated, output voltage that may fall within the range of variability of the input voltage to power a load. For example, the range of the input voltage source may be four to six volts, and the regulated output voltage may be 5 volts. Thus, under one operating condition the power converter boosts the input voltage to produce the output voltage, and under another operating condition the power converter bucks the input voltage to produce the output voltage. To provide the voltage conversion and regulation functions, the power converters include active power switches such as metal-oxide semiconductor field-effect transistors (“MOSFETs”) that are coupled to the voltage source and periodically power switch a reactive circuit element such as an inductor to the voltage source at a power switching frequency that may be on the order of five megahertz.
However, a feedback process to control a power switch in a power converter employing a buck power conversion topology produces opposite control signal changes of a comparable feedback process for a power converter employing a boost power conversion topology. In addition, a power converter configured to operate in either a buck or a boost power conversion mode experiences a discontinuity in the control process related to inherent inefficiencies in a practical circuit during transitions between buck and boost power conversion modes. Thus, the problem of controlling a power converter that may be operable in a buck or a boost power conversion mode depending on a relationship between input and output voltages thereof remains an unresolved issue.
Accordingly, what is needed in the art is a controller for a power converter and related method that can operate in different power conversion modes that overcomes deficiencies in the prior art.